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The present invention relates to a eutectic Alxe2x80x94Si alloy having excellent free machinability and abrasion resistance. In the present invention, the free machinability means that machinability is excellent.
The inventive eutectic Alxe2x80x94Si alloy can be applied to parts requiring formability, workability and abrasion resistance, such as scrolls or pistons of compressors for air conditioners in automobiles or appliances.
Lubricants should be continuously fed to friction face of scrolls or pistons. Otherwise, seizure between friction metals occurs. So, metal materials having excellent abrasion resistance as well as formability and workability are suitable for use in such parts.
On the other hand, in order to manufacture lightweight automobiles or appliances, metals having low specific gravity are used. Also, even though metals are excellent in abrasion resistance and have low specific gravity, if they have poor workability including machinability, preparation cost becomes high. Metals, such as cast iron or bronze, have the advantage of excellent machinability but suffer from the disadvantage of high specific gravity. Therefore, in recent years, Al-based alloys are widely used. Excellent ductility of these metals results in improved formability.
Typically, there is a representative eutectic Alxe2x80x94Si alloy having excellent abrasion resistance, lightweight property, and relatively superior formability and workability, as shown in the following
Such alloy is called A4032 alloy in the related fields.
In alloys comprising two or more metals, the metals which are able to produce a congruent compound are used stoichiometrically, in which the congruent compound refers to that one metal of solid phase which is melted in the other metal of liquid phase at melted state or solid solution state. The alloy forming the congruent compound appears to be in equilibrium state.
The alloy which consists of compositions forming the congruent compound is called a eutectic alloy, in which the eutectic alloy exists at the eutectic point in equilibrium diagrams of alloys. Alloys which are positioned at the left side of eutectic point in the equilibrium diagram are referred to as hypo-eutectic alloys, and alloys located at the right side of eutectic point in the diagram are called hyper-eutectic alloys.
As for Alxe2x80x94Si alloy, alloys having 12.5 wt % of Si correspond to congruent compounds. Commonly, if Si content ranges from 11 to 13 wt % , such alloy is called a eutectic alloy. On the other hand, hypo-eutectic alloys have Si content less than said range and hyper-eutectic alloys have Si content higher than said range.
In the case of applying to pistons in compressors for automobile air conditioners, conventional A4032 eutectic alloys representatively used in this field are subject to surface-treatment, such as anodizing or Sn plating, to improve abrasion resistance. Such conventional alloy is disadvantageous in that, unless lubricants are smoothly fed onto friction faces, seizure between the metals occurs. As well, cutting workability becomes poor and abrasion ratio of cutting tools is very high, thus increasing preparation cost.
There is thus a widely recognized need for materials having superior machinability and abrasion resistance to conventional A4032 alloy.
It is an object of the present invention to provide a eutectic Alxe2x80x94Si alloy, which is excellent in free-machinability and abrasion resistance and maintains high strength through heat treatment.
The intensive and thorough research on a eutectic Alxe2x80x94Si alloy, carried outby the present inventors aiming to avoid the problems encountered in the prior arts, resulted in the finding that, on preparation of a eutectic Alxe2x80x94Si alloy, Sb, not reactive with Bi, is added, along with Bi, under conditions that Sr, strongly reactive with Bi, is not used, and amounts of Mg, Mn and Ni to be added are minimized, yielding Alxe2x80x94Sixe2x80x94Cuxe2x80x94Bi alloy, whereby eutectic Alxe2x80x94Si alloys which have superior free-machinability, abrasion resistance and ductility to conventional eutectic Alxe2x80x94Si alloys, and maintain high strength though heat treatment, can be obtained.
As for conventional eutectic Alxe2x80x94Si alloys, there was no alloy containing Sb as a component.